The kinesin-like spindle protein Eg5, also known as KSP and Kif11, is a motor protein that is essential for establishing a bipolar spindle during mitosis. Eg5-I is a potent inhibitor of Eg5, both in vitro and in cells (IC50s = 127 and 190 nM, respectively). It is an analog of S-trityl-L-cysteine (STLC), but is more potent and has better solubility than STLC. Eg5-I blocks bipolar spindle formation and inhibits the growth of cancer cells, with an average GI50 value of 360 nM against a broad panel of tumor cells (GI50 range = 10 nM to 3 μM). It ranges from 140- to 1200-fold more potent against cancer cells than monastrol , which also acts by inhibiting Eg5.
